Atherosclerotic vascular disease, one of the major causes of death in Western society, results from complex interactions between multiple genetic and environmental factors. With the long term goals of dissecting some of the molecular details of atherogenesis and of generating small animal models of human atherosclerosis, we have been using gene targeting in mice. During the last grant period, we generated five mutants and proved that the introduction of mutations into lipid metabolism-related genes of otherwise normal mice can produce atherosclerosis and is an exciting and informative new approach to understanding the role of genetic factors in atherogenesis. Two approaches will be used during the next five years. The first will focus on using gene targeting to introduce specific alterations into genes important in lipid transport rather than simply inactivating them. The second will focus on studying combinations of single gene defects so as to "synthesize" the complex genetic disease of atherosclerosis from components that singly are not atherogenic. Specific aim 1 is to generate mice that produce apolipoprotein B100 having altered amino acid sequences at the predicted LDL receptor binding sites. We expect that the resulting mice will accumulate dysfunctional LDL particles in their plasma, and will therefore become susceptible to atherosclerosis. Specific aim 2 is to generate mice that produce human apoE isoforms in place of mouse apoE. Mice producing human apoE2 in the natural chromosomal context, when compared to mice producing human apoE3 at the same location, should help in understanding the etiology of the Type III hyperlipoproteinemia associated with the human apoE2 allele. Specific aim 3 is to investigate the effects of combining single gene defects by using gene targeting to generate mice with apoAI/apoCIII and apoAI/apoCIII/apoAIV deficiencies which in humans cause premature atherosclerosis. Specific aim 4 is to generate, by breeding, mice carrying various other combinations of mutations. We expect that studies of the consequences in mice of modification of genes involved in lipid metabolism, both singly and in combinations, will greatly increase our understanding of atherogenesis.